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Structure of anthrax lethal toxin prepore complex suggests a pathway for efficient cell entry

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ABSTRACT

Anthrax toxin is a tripartite complex in which the protective antigen moiety forms a pore through which lethal factor and edema factor are translocated. Fabre et al. reveal a mechanism for efficient translocation in their structure of the heptameric protective antigen prepore bound to three lethal factors.

No MeSH data available.


Related in: MedlinePlus

Compatibility of our model with previous structures. (A) Comparison of the prepore and pore rims. Domains 1a and 3 from the prepore (cyan/orange) and pore (blue/red) are overlaid. The RMSDon Cαs for the top of the rim (seven domains 1a, residues 176–250) and the rim (seven domains 1a and 3, residues 176–250 + residues 458–496) is 1.48 Å. The black ring denotes the outer limit of LF contacts, and the blue “N”s denoted the innermost contacts. (B) Hypothetical model of an assembly intermediate, a PA83–PA63–LF complex. Starting with a (PA63)2–LF moiety extracted from our EM structure, the location of PA20 was predicted by overlaying the crystal structure of domain 1 of full-length PA83 onto domain 1a of the counterclockwise PA63 protomer, creating a new PA83 protomer (shown in orange and red; as described as in Material and methods section Modeling the (PA63)7–(LF)3 complex). No major steric clashes were observed between the new PA20 moiety and the clockwise PA63 protomer (green), which makes the major interactions with LF. However, only the closed conformer of LF is compatible with the presence of PA20. The circled “N” marks the first ordered helix of closed LF, which is sterically occluded from reorganizing and entering the channel pore. The yellow dashed line indicates novel interfaces that could stabilize the intermediate.
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fig7: Compatibility of our model with previous structures. (A) Comparison of the prepore and pore rims. Domains 1a and 3 from the prepore (cyan/orange) and pore (blue/red) are overlaid. The RMSDon Cαs for the top of the rim (seven domains 1a, residues 176–250) and the rim (seven domains 1a and 3, residues 176–250 + residues 458–496) is 1.48 Å. The black ring denotes the outer limit of LF contacts, and the blue “N”s denoted the innermost contacts. (B) Hypothetical model of an assembly intermediate, a PA83–PA63–LF complex. Starting with a (PA63)2–LF moiety extracted from our EM structure, the location of PA20 was predicted by overlaying the crystal structure of domain 1 of full-length PA83 onto domain 1a of the counterclockwise PA63 protomer, creating a new PA83 protomer (shown in orange and red; as described as in Material and methods section Modeling the (PA63)7–(LF)3 complex). No major steric clashes were observed between the new PA20 moiety and the clockwise PA63 protomer (green), which makes the major interactions with LF. However, only the closed conformer of LF is compatible with the presence of PA20. The circled “N” marks the first ordered helix of closed LF, which is sterically occluded from reorganizing and entering the channel pore. The yellow dashed line indicates novel interfaces that could stabilize the intermediate.

Mentions: In our model, the binding footprint of LFN, which spans two sequential PA63 protomers, is fully consistent with the binding mode observed in the octameric prepore bound to LFN (Feld et al., 2010), as well as earlier models from Collier’s group based on an elegant series of mutagenesis experiments (Cunningham et al., 2002; Lacy et al., 2002) and our modeling experiments (Alisaraie and Rouiller, 2016). The surface of PA63 that interacts with LF is preserved between the octamer and the heptamer. A comparison of the two adjacent PA63 subunits in the heptamer and octamer indicates an RMSDon Cαs of 1.07 Å (domains 1a and 3). Of particular note, the LF-binding surface on the (PA63)7 surface is strongly conserved upon conversion of the heptamer from prepore to pore (Fig. 7 A), despite the large motions of domain 2, in particular, which leads to formation of the Φ-clamp and membrane-spanning translocation channel (Jiang et al., 2015). Therefore, we expect the packing between LF and PA observed in our study to be preserved during the transition from prepore to pore.


Structure of anthrax lethal toxin prepore complex suggests a pathway for efficient cell entry
Compatibility of our model with previous structures. (A) Comparison of the prepore and pore rims. Domains 1a and 3 from the prepore (cyan/orange) and pore (blue/red) are overlaid. The RMSDon Cαs for the top of the rim (seven domains 1a, residues 176–250) and the rim (seven domains 1a and 3, residues 176–250 + residues 458–496) is 1.48 Å. The black ring denotes the outer limit of LF contacts, and the blue “N”s denoted the innermost contacts. (B) Hypothetical model of an assembly intermediate, a PA83–PA63–LF complex. Starting with a (PA63)2–LF moiety extracted from our EM structure, the location of PA20 was predicted by overlaying the crystal structure of domain 1 of full-length PA83 onto domain 1a of the counterclockwise PA63 protomer, creating a new PA83 protomer (shown in orange and red; as described as in Material and methods section Modeling the (PA63)7–(LF)3 complex). No major steric clashes were observed between the new PA20 moiety and the clockwise PA63 protomer (green), which makes the major interactions with LF. However, only the closed conformer of LF is compatible with the presence of PA20. The circled “N” marks the first ordered helix of closed LF, which is sterically occluded from reorganizing and entering the channel pore. The yellow dashed line indicates novel interfaces that could stabilize the intermediate.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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fig7: Compatibility of our model with previous structures. (A) Comparison of the prepore and pore rims. Domains 1a and 3 from the prepore (cyan/orange) and pore (blue/red) are overlaid. The RMSDon Cαs for the top of the rim (seven domains 1a, residues 176–250) and the rim (seven domains 1a and 3, residues 176–250 + residues 458–496) is 1.48 Å. The black ring denotes the outer limit of LF contacts, and the blue “N”s denoted the innermost contacts. (B) Hypothetical model of an assembly intermediate, a PA83–PA63–LF complex. Starting with a (PA63)2–LF moiety extracted from our EM structure, the location of PA20 was predicted by overlaying the crystal structure of domain 1 of full-length PA83 onto domain 1a of the counterclockwise PA63 protomer, creating a new PA83 protomer (shown in orange and red; as described as in Material and methods section Modeling the (PA63)7–(LF)3 complex). No major steric clashes were observed between the new PA20 moiety and the clockwise PA63 protomer (green), which makes the major interactions with LF. However, only the closed conformer of LF is compatible with the presence of PA20. The circled “N” marks the first ordered helix of closed LF, which is sterically occluded from reorganizing and entering the channel pore. The yellow dashed line indicates novel interfaces that could stabilize the intermediate.
Mentions: In our model, the binding footprint of LFN, which spans two sequential PA63 protomers, is fully consistent with the binding mode observed in the octameric prepore bound to LFN (Feld et al., 2010), as well as earlier models from Collier’s group based on an elegant series of mutagenesis experiments (Cunningham et al., 2002; Lacy et al., 2002) and our modeling experiments (Alisaraie and Rouiller, 2016). The surface of PA63 that interacts with LF is preserved between the octamer and the heptamer. A comparison of the two adjacent PA63 subunits in the heptamer and octamer indicates an RMSDon Cαs of 1.07 Å (domains 1a and 3). Of particular note, the LF-binding surface on the (PA63)7 surface is strongly conserved upon conversion of the heptamer from prepore to pore (Fig. 7 A), despite the large motions of domain 2, in particular, which leads to formation of the Φ-clamp and membrane-spanning translocation channel (Jiang et al., 2015). Therefore, we expect the packing between LF and PA observed in our study to be preserved during the transition from prepore to pore.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Anthrax toxin is a tripartite complex in which the protective antigen moiety forms a pore through which lethal factor and edema factor are translocated. Fabre et al. reveal a mechanism for efficient translocation in their structure of the heptameric protective antigen prepore bound to three lethal factors.

No MeSH data available.


Related in: MedlinePlus